The present invention relates to an image forming apparatus.
In the image forming apparatus of the electrophotographic method, there is carried out image quality control where a toner image of a reference pattern is formed on an image carrier such as a photoconductive substance and an image density of the toner image is detected by an image sensor then the detected result is fed back to image forming conditions.
By such image quality control, effects caused by a change of an environment or a change of characteristic of each component configuring the image forming apparatus are eliminated and a high quality image is consistently formed.
In the above image control, an output characteristic of the density sensor such as sensitivity heavily affects the control.
Therefore, countermeasures to cope with a fluctuation of the density sensor used in image quality control are suggested.
In unexamined Japanese Patent Application Publication No. 2000-81739, it is suggested that an output of the density sensor is compensated based on an effect of change of amount of light emitted from a light emitting element configuring the density sensor, and an effect of a change of a surface condition of the image carrier on which the reference pattern is formed.
In unexamined Japanese Patent Application Publication No. 2000-267369, it is suggested that by providing a detection device for an amount of emitted light in the density sensor, a detection accuracy for the change of amount of emitted light is enhanced and the output of the density sensor is compensated.
In unexamined Japanese Patent Application Publication No. 2002-236402, it is suggested that using a regular reflection type density detection device and a diffusion reflection type density detection device, the output of the diffusion reflection type density detection device is compensated based on output values of the regular reflection type density detection device and the diffusion reflection type density detection device.
As above, various compensations for the density detected by the density sensor are suggested. As to elimination or suppression of the fluctuation, some technologies have solved by analyzing the change with time of the density sensor and factors of the fluctuation of the density sensor as the above publications study. However, as to variations of the density sensors due to the individual differences, the image forming apparatus is operated to form an image and the compensation is carried out by detecting the density of the output image.
In this case the fluctuation of the sensor outputs are reflected by an individual difference of the image forming device of the image forming apparatus and an individual difference of the whole image forming section of the image forming apparatus such as an individual difference of a reflection coefficient of the image carrier besides an individual difference of the density sensor. Conventionally compensation of such output fluctuations of the density sensor was carried out as follow through image forming.
More specifically, the image quality control, where a patch image is formed, the density of the patch image is detected by the density sensor and the result of detection is fed back to image forming, is carried out, thereafter the image is formed on a recording material.
Then the density of the image on the recording material is measured by a density meter or a calorimeter so that the density sensor is adjusted and the measurement becomes consistent.
As above, conventionally, the compensation for the fluctuation of the density sensor output used in the image quality control is carried out based on the measurement result by actually outputting the image on the recording material and measuring the density through a density meter or the calorimeter. Compensate is time consuming, and since automation of the compensation is difficult, a manufacturing cost and a maintenance cost increase.